Method of treating acrylonitrile synthetic fibers



United States Patent 12 Claims. i0]. s ss The present invention relates to a process for preventing the uneven dyeing and/ or improving the whiteness stability of acrylonitrile synthetic fiber containing at least 85% by weight of acrylonitrile by treating the same with an aqueous solution of a multivalent metallic salt so as to restrain the rate of dyeing of same with cationic dyestuffs.

The dyeing of an acrylonitrile synthetic fiber with a cationic dyestuff has a serious disadvantage, for the rate of dyeing is so high that uneven dyeing results when the substrate must be dyed light or medium shades. It is known that uneven dyeing can be prevented by adding a cationic surface active agent to a dye bath as a retarding agent to reduce the dyeing rate. This phenomenon may be explained by the concept of competition between dyestufi and surfactant for active sites on the substrate. According to this theory, the dyeing rate should have to be reduced by the presence of two rivalling factors if a cation other than the dyestuif is present in the fiber. Actually, ordinary cations are relatively slow in penetrating the fibrous structure while the dyest-utf may diffuse into the fiber so rapidly that no retarding occurs where such cations are added to the dye bath. Should the aforementioned theory hold true under certain circumstances, however, it is reasonable to expect that dyeing will be retarded when such cations are preliminarily incorporated in the fiber at a stage prior to the dyeing operation.

With the foregoing in mind, we have found that dyeing may be successfully retarded by pre-treating the fiber with an aqueous solution of a polyvalent metallic salt before the dyeing of same. In this connection, it has also been found that the metallic ion so added will not be elfective unless it is bivalent or higher instead of univalent. Another discovery is that when the fiber is thus treated with a multivalent metal salt, the stability of whiteness of the fiber is also improved. Heretofore, various processes have been proposed for improving the whiteness of acrylonitrile synthetic fibers, but most of them are not conducive to the stability of whiteness even if the degree of whiteness is improved. Thus, being heated as in a wetthermal treatment, the fiber is prone to discoloration. However, the fiber treated with multivalent metallic salt of the mentioned type according to this invention does not discolor even after prolonged exposure under hot wet conditions; therefore said treatment improves the stability of whiteness of the fiber, although the underlying mechanism has not yet been theoretically established. Metallic salts which exhibit strong acidity but no color upon being dissolved in water, e.g., aluminum salts, are particularly suited for the purposes stated.

To describe the invention in further detail, the fiber spun from an acrylonitrile polymer dyeable with cationic dyestuffs and containing at least 85% by weight of acrylonitrile is treated with an aqueous solution of a multivalent metallic salt, preferably an aluminum salt, at any desired stage of processing from after spinning to the final fiber, and preferably during a stage wherein the fiber is still in a wet gelled state. The preferred concentration of such a metallic salt is from 0.0001 mole/liter to 0.1 mole/ liter; for if the salt is present in a concentration of more than 0.1 mole/ liter, the effect obtainable will not be proportional to the gain in concentration, the net result being "Ice such that not only economy is sacrificed but depending upon the type of metallic salt, unduly high concentrations may impart objectionable color to the treated fiber. The pH of the aqueous solution is preferably from 2 to 4. Those metallic salts which do not exhibit acidity or which are only weakly acidic in water may be adjusted to a suitable pH by adding an acid to the solution. Though the optimum pH range varies according to the type and concentration of salt, pH values over 5 could impair the whiteness of fiber and should, therefore, be avoided. It is preferable that the treatment he eifected over a sufficiently long period of time, but it may be shortened, if required, by increasing the salt concentration or the treating temperature, or both. Since the treating solution can penetra-te easily into a gelled swollen fiber containing water, such a fiber can be satisfactorily treated at room temperature in a matter of seconds. In contrast, it takes several to scores of minutes at high temperatures .in the case of hot stretched fiber which is hard to penetrate. Care must be used, however, for the treatment for a sustained time at high temperature might be detrimental to the whiteness of the fiber.

The polymers to which the present invention is applicable are not limited to polyacrylonitrile (homopolymer) but may be any member of the group consisting of those copolymers, graft polymers, and block polymers composed of acrylonitrile and at least one monoethylene-type monomer copolymerizable therewith and containing more than by weight of acrylonitrile. In addition, it is necessary that these polymers must contain acid groups which can act as dye sites for cationic dyestatfs.

The monoethylene-type monomers copolymerizable with acrylonitrile include, for example, acrylic acid esters, methacrylic acid esters, vinyl acetate, styrene, vinylchloride, methacrylonitrile, etc., acrylic acid, methacrylic acid, allylsulfonic acid, methalylsulfonic acid, styrene-sulfonic acid, etc. and the salts thereof.

The multivalent metallic salts which can be employed in the process of the invention include, for example, inorganic salts such as the nitrates, sulfates, chlorides, etc. of alkaline earth metals such as magnesium, calcium, barium, etc. of transition metals such as chromium, zinc, c0- balt, nickel, etc., or of such other metals as aluminum, tin, lead, etc., as well as the salts of said metals and organic acids, it being understood that said salts must be soluble in water.

The invention will be further illustrated by reference to the following examples, wherein all percentages given are by weight and the dyeing tests and the measurements of yellowness were made in the following manner:

DYEING TEST: DYESTUFFfiSEVRON BRILLIANT RED 4G (E. I. DU PONT DE NEMOURS & CO.)

Samples were dyed in a bath composed of a suitable amount of Sevron'Brilliant Red 4G (E. I. du Pont de Nemours & Co.), 1% O.W.F. of acetic acid, and 3% O.W.F. of sodium acetate at a bath ratio of to 1 and a bath temperature of 98 C. The exhaustion of dyestuif was colorimetrically determined based on the residual liquor.

MEASUREMENT OF YELLOWNESS Yellowness wherein R R and R are the percent reflectance solution (pH 3) of nitric acid at room temperature for 15 seconds. The filament was then stretched under heat, heat-treated, and dried as in Example 1. Upon treatment with an aqueous solution of aluminum nitrate, the filament had improved retarding effect and stability of Whitecompared as to yellowness. ness.

Dye adsorption Yellowness (percent) Gel treatment min. 60 min. Raw Boiling filament A Aluminum nitrate 0.0013 mole/l.

pH 42.8 85 7 2.0 4 7 B Aluminum nitrate 0 013 mole/l p113 35. 0 71. 8 1. 2 3. 8 C Nitricacid pH 3 93.4 99.6 7.2 10.2

(Dyestuff concentration in dye bath: 4% O.W.F.)

Example 1 Example 3 A copolymer composed of 90% of acrylonitrile, 10% of methyl acrylate and less than 1% of methacryl sulfonate was spun in the same manner as in Example 1. The resulting gelled filament was treated with an aqueous solution of aluminum nitrate (Sample A: 0.001 mole/ liter, pH 3; Sample B: 0.01 mole/liter, pH 3; Sample C: 0.1 mole/liter, pH 3) or an aqueous solution (pH 3) of nitric acid as in Example 1. The filament was then after-treated.

Dye adsorption (percent) Yellowness Gel treatment 10 min. 30 min. 60 min. Raw Boiling filament A Aluminum nitrate 0.001 mole/1.

pH 3 63. 1 98. 4 99. 5 3. 2 7. 6 B Aluminum nitrate 0.01 mole/l.

pH 3 50.0 95. 2 99. 6 3. 6 6. 3 C Aluminum nitrate 0.1 mole/1., pH 3., 43. 7 87. 6 99. 0 3. 3 6. 2 D Nitric acid pH 3 97. 1 99.8 99. 8 3. 2 11. 6

(Dyestuff concentration in dye bath: 4% O.W.F.)

pH 2, (D) 0.01 mole/liter, pH 4] or (B) an acid aqueous solution (pH 3) of nitric acid, for about 15 seconds at room temperature. Thereafter, the filament was stretched under heat and heat-treated. The filament was finally dried.

It was observed that both the retarding effect and the stability of whiteness has been improved.

Example 4 Each sample of the gelled filament spun from a copoly- Dye adsorption (percent) Yellowncss Gel treatment Raw Boiling Bleaching Boiling 10 min. 30 min. min. filament after bleach.

0.001 mole/l. aluminum nitrate pH 2. 91. 3 99. 3 99. 5 4.0 7. 9 3. 2 11.9 0.001 mole/l. aluminum nitrate pH 4 66. 0 98. 3 99. 5 4. 3 7. 4 2. 8 8. 6 0.01 mole/l. aluminum nitrate pH 2. 66. 8 98. 3 99. 4 4. 0 6. 4 2. 3 9. 5 0.01 mole/l. aluminum nitrate pH 4 64. 1 92. 4 99. 3 3. 2 6. 2 1. 6 8. 8 Nitric acid pH 3 96. 7 99. 5 99. 5 7. 4 9. 8 2. 0 15. 8

(Dyestutf concentration in dye bath: 4% O.W.F.)

Example 2 mer similar to the one employed in Example 1 was treated with an aqueous solution of zinc nitrate (Sample A: 0.01

mole/liter, pH 2; Sample B: 0.01 mole/liter pH 4) or an aqueous solution (pH 6) of nitric acid under the same conditions as in Example 1. The filament is then drawn 5 under heat and after-treated.

Dye adsorption (percent) Yellowness Gel treatment 10 30 60 Raw fila- Boiling min. min. min. Inent Boiling Bleaching after bleach Zinc nitrate 0.01 mole/l. pH 2 65. 9 95. 9 98. 8 5.6 8. 4 1. 9 11. 5 Zinc nitrate 0.01 mole/l. pH 4 61. 91. 1 98. 8 l2. 3 l3. 0 2. 0 14. 4 Nitric acid pH 3 95. 3 99. 4 99. 5 5. 8 10. l 2. 3 15, :3

(Dyestufi: 2% O.W.F.)

The filament treated with an aqueous solution of zinc 5. A process as defined in claim 1 wherein said multinitrate suffered a loss in the stability of whiteness at high concentrations. Thus, it is advantageous to select lower pH values. Sample A was better than Sample C in retarding effect and the stability of whiteness.

Example 5 Samples of the filament spun from a copolymer similar to the one employed in Example 1, drawn under heat, and then heat-treated were treated with an aqueous solution of (\A) aluminum nitrate (-0.03 mole/liter, pH 3), (B) zinc nitrate (0.03 mole/liter, pH '3), respectively, at the temperature of 98 C. for 40 minutes. The results of dyeing tests for these samples and a control are summarized below. While a slight fading was observed on Samples A and B, the shade itself was not affected.

valent metallic salt is aluminum nitrate.

6. A process as defined in claim 1 wherein said multivalent metallic salt is zinc nitrate.

7. In the process of producing dyed fibers from an acrylonitrile polymer fiber containing acid groups and which is highly substantive to cationic dyes comprising spinning said polymer from a solution thereof into a suitable coagulating medium to form a Wet gelled filament, drying said wet gelled filament, and dyeing the filament with a cationic dye; the improvement comprising treating the filament after spinning and prior to dyeing with an aqueous solution of a water-soluble salt of a multivalent metallic ion selected 'from the group consisting of magnesium, calcium, barium, chromium, zinc, cobalt, nickel, aluminum, tin, and lead with an anion selected from the Dye adsorption (percent) Example 6 Samples of the filament spun from a copolymer similar to the one employed in Example 1 drawn under heat and then heat-treated were treated with an aqueous solution (0.01 mole/liter) of sodium nitrate, potassium nitrate, calcium nitrate, barium chloride, nickel nitrate, and aluminum sulfate, respectively, at the temperature of 100 C. for '30 minutes. While no retarding effect was observed with the samples treated with sodium nitrate and potassium nitrate respectively, the other multivalent metallic salts showed a conspicuous retarding effect.

We claim:

1. A process for retarding the dyeability of an acrylonitrile polymer fiber containing acid groups and which is highly substantive to cationic dyes, said process comprising immersing such fiber in an aqueous solution of a water-soluble salt of a multivalent metallic ion selected from the group consisting of magnesium, calcium, barium, chromium, zinc, cobalt, nickel, aluminum, tin, and lead with an anion selected from the group consisting of nitrates, sulfates, chlorides, and organic acid residues prior to exposure of such fiber to cationic dyes.

2. A process as defined in claim 1 wherein said aqueous solution has a salt concentration of between 0.0001 mole/ liter and 0.1 mole/liter.

3. A process as defined in claim 1 wherein said aqueous solution is maintained at a pH between about 2 and about 4.

4. A process as defined in claim 1 wherein said fiber is immersed in said aqueous solution after spinning while still in the wet gel state.

group consisting of nitrate ganic acid residues.

8. A process as defined in claim 7 wherein the filament is treated with the aqueous solution of a watersoluble multivalent metallic salt while the filament is in the wet gelled state.

9. A process as defined in claim 7 wherein said aqueous solution is maintained at a pH between about 2 and about 4.

10. A fiber produced by the process of claim 1.

11. A fiber produced by the process of claim 5.

12. A fiber produced by the process of claim 6.

s, sulfates, chlorides, and or- Refereuces Cited by the Examiner UNITED STATES PATENTS 2,869,968 1/ 1959 Thummel et a1 8-21 2,984,912 5/ 19 61 Robertson et al. 3,014,776 12/ 1961 Mecco 8--115.-5 3,053,609 9/ 1962 Miller. 3,061,398 10/1962 Veitch. 3,117, 831 1/1964 Mautner. 3,123,432 5/ 1964 Webb 8115.5

OTHER REFERENCES Neary et al.: American Dyestufi Reporter, vol. 46, No. 17, August 26, 1957, pages 625-33.

NORMAN G. TORCHIN, Primary Examiner.

ABRAHAM H. WINKEISTEIN, Examiner. I. C. CANNON, Assistant Examiner. 

1. A PROCESS FOR RETARDING THE DYEABILITY OF AN ACRYLONITRILE POLYMER FIBER CONTAINING ACID GROUPS AND WHICH IS HIGHLY SUBSTANTIVE TO CATIONIC DYES, SAID PROCESS COMPRISING IMMERSING SUCH FIBER IN AN AQUEOUS SOLUTION OF A WATER-SOLUBLE SALT OF A MULTIVALENT METALLIC ION SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM, CALCIUM, BARIUM, CHROMIUM, ZINC, COBALT, NICKEL, ALUMINUM, TIN, AND LEAD WITH AN ANION SELECTED FROM THE GROUP CONSISTING OF NITRATES, SULFATES, CHLORIDES, AND ORGANIC ACID RESIDUES PRIOR TO EXPOSURE OF SUCH FIBER TO CATIONIC DYES. 